Pontoon Boat & Deck Boat Forum

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Sorry, someone asked me to relay what battery tender told me... talked to them several days back. I was told it is completely normal for the battery tender plus to get very warm when charging... and then should start to cool off when the tender goes to the green " charged " light.

Some quick comments:

A "dead" battery is 10.5v under load for most lead-acid batteries including Flooded, Gel and AGM batteries.
Think about it like red line on a tach. Can you go there? Sure, but not for too long. Can you go past it? Sure, if you want to cause damage......
When you reach 10.5v under load, the battery has provided all of the energy that it was designed to do.

BUT - a "dead" battery is 11.5v to 11.6v with no load or charging for the previous 6 hours at least.
If you pull a battery down to 10.5v with a load on it (heavy or light), then shut off the load and let the battery rest, it will rebound to 11.5v to 11.6v.
Yes, you can turn the loads back on drag it all the down to 0v if you try hard!

Battery charging is more complex than discharging, and the "best" way to do it depends upon the specific battery. Some batteries NEED to be charged slowly and others very hard and fast in order to stay healthy. True deep cycle are different than Marine which are different than starting..........and battery chemistry throws in some twists.

But in general a small charger will eventually charge a big battery - within reason. Look at it like a rain barrel open to the sky. Will a light rain eventually fill the barrel? Yup, as long as the rain exceeds the evaporation (the battery self discharge rate) rate.

Very few marine/RV/aircraft batteries die young from overcharging, but MOST die from undercharging and sulfation...... Ever see a "bulging/splitting" battery? That's undercharging at it's finest!

I'll avoid being like the Energizer Bunny and stop for now.

Marc